Advertisements

"Alfred Molon" <> wrote in message
news:...
> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
> Neptune etc., what exposure time would be necessary to take a photo at
> ISO 100 and F4 or F8 ?

This very question has been causing me sleepless nights for years... I do
hope someone can answer it soon!

The light falls off as the square of the distance. Find a chart of
planetary distances in AUs (one AU is radius of earth orbit). Or,
convert from miles (1 AU = 93,000,000 miles). Now, square the number
of AUs, this is the factor the earth exposure time must be multiplied
by.

As an example, I believe mars is about 2 AU. Thus one must make an
exposure four times what it would be on earth.

"Jürgen Exner" <> writes:
> Alfred Molon wrote:
>> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
>> Neptune etc., what exposure time would be necessary to take a photo
>> at ISO 100 and F4 or F8 ?
>
> Exactly the same as on earth: long enough to not underexpose, short
> enough to not overexpose.
>
> Or are you asking about how much light each planet recieves from the
> sun?

Mars averages about 1.5 times as far from the Sun as Earth;
log2(1.5^2) is about 1.17, so you'd need to be marginally more than a
stop slower than for otherwise equivalent conditions on Earth. "Sunny
11" perhaps.

Venus would be about a stop faster, if it weren't for the thick clouds
that cover the entire planet.

On Sun, 01 Jul 2007 12:35:15 GMT, "Rudy Lacchin"
<> wrote:
>
>"Alfred Molon" <> wrote in message
>news:...
>> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
>> Neptune etc., what exposure time would be necessary to take a photo at
>> ISO 100 and F4 or F8 ?
>
>This very question has been causing me sleepless nights for years... I do
>hope someone can answer it soon!
>

Don't knock the question. Given the current flood of "what
camera/lens/gadget/ etc for under blah blah..." posts a truly original
question deserves some respect.

Now if I was going to go to the trouble and expense of booking a tour
of say Io (limited accommodations but spectacular volcanic scenery)
I'd also invest in a camera with a long wavelength sensor--InAs, InSb
MCT, that type. In sunlight the special camera's infrared response
would cut exposure time by about a factor of 3 but once Io swung
behind Jupiter you'll get some spectacular nighttime pics using the IR
radiation from the glowing sulfur and lava.

Alfred Molon wrote:
> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
> Neptune etc., what exposure time would be necessary to take a photo at
> ISO 100 and F4 or F8 ?

Assuming you wanted to expose an 18% gray card, then
the exposure would be the square of the relative distance
of the planet from the sun compared to the earth.
Don's answer is the only correct one I've seen so far in this
thread.

If you want to expose for the average scene brightness
on that planet (or moon), then you also need to take into
account the reflectivity of the planetary surface, and if
it has an atmosphere, the absorption of sunlight through
the atmosphere.

For example, Saturn is 9.5 times further from the sun than
the earth, so sunlight is 9.5*9.5 times fainter, or about
90. So sunny f/16 rule on earth becomes about sunny f/1.8
on Saturn. But on the Icy moons, the reflectivity is near
100% so you gain about 5x in brightness, so exposures would
be more like sunny f/4 rule. But on dark moons like Phoebe,
where reflectivity is only a couple percent, you lose
another factor of 10 over an 18% gray card, so the rule
becomes about sunny f/0.5! On Titan, the situation is made
difficult by the thick smog in the atmosphere, cutting a lot
of sunlight at Titan's surface.

JPC's idea of using infrared doesn't work. Sunlight peaks in the
visible part of the spectrum. Going into the infrared, there
are less photons. In the outer solar system, the bodies are colder
than earth, so emit less thermal radiation than the earth,
so exposure times are long in the infrared too.

Going to Venus or Mercury, you have more light, so exposure
times are shorter, if you can keep your camera from melting!

On Sun, 01 Jul 2007 14:04:51 -0600, "Roger N. Clark (change
username to rnclark)" <> wrote:
>Alfred Molon wrote:
>> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
>> Neptune etc., what exposure time would be necessary to take a photo at
>> ISO 100 and F4 or F8 ?
>
>Assuming you wanted to expose an 18% gray card, then
>the exposure would be the square of the relative distance
>of the planet from the sun compared to the earth.
>Don's answer is the only correct one I've seen so far in this
>thread.
>
>If you want to expose for the average scene brightness
>on that planet (or moon), then you also need to take into
>account the reflectivity of the planetary surface, and if
>it has an atmosphere, the absorption of sunlight through
>the atmosphere.

So you think the planetary atmosphere wouldn't affect a 18%
grey card?

Or did you mean exposing from a grey card in space at the
same distance drom the sun as the planet - which isn't what
the OP asked.

Like I said earlier, piece of string until some more
parameters are defined.

John Bean wrote:
> On Sun, 01 Jul 2007 14:04:51 -0600, "Roger N. Clark (change
> username to rnclark)" <> wrote:
>
>> Alfred Molon wrote:
>>> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
>>> Neptune etc., what exposure time would be necessary to take a photo at
>>> ISO 100 and F4 or F8 ?
>> Assuming you wanted to expose an 18% gray card, then
>> the exposure would be the square of the relative distance
>> of the planet from the sun compared to the earth.
>> Don's answer is the only correct one I've seen so far in this
>> thread.
>>
>> If you want to expose for the average scene brightness
>> on that planet (or moon), then you also need to take into
>> account the reflectivity of the planetary surface, and if
>> it has an atmosphere, the absorption of sunlight through
>> the atmosphere.
>
> So you think the planetary atmosphere wouldn't affect a 18%
> grey card?
>
> Or did you mean exposing from a grey card in space at the
> same distance drom the sun as the planet - which isn't what
> the OP asked.
>
> Like I said earlier, piece of string until some more
> parameters are defined.
>
Do you go out into space with a gray card to determine exposure on
earth? No. The gray card takes care of local atmospheric conditions etc
at the time of the reading. Otherwise, you could just set one
f/stop/shutter speed combination to for all pictures on Earth--cloudy
day, high noon, midnight, snow storm, etc.
Allen

In article <>, Roger N. Clark (change username
to rnclark) says...
> For example, Saturn is 9.5 times further from the sun than
> the earth, so sunlight is 9.5*9.5 times fainter, or about
> 90. So sunny f/16 rule on earth becomes about sunny f/1.8
> on Saturn. But on the Icy moons, the reflectivity is near
> 100% so you gain about 5x in brightness, so exposures would
> be more like sunny f/4 rule. But on dark moons like Phoebe,
> where reflectivity is only a couple percent, you lose
> another factor of 10 over an 18% gray card, so the rule
> becomes about sunny f/0.5! On Titan, the situation is made
> difficult by the thick smog in the atmosphere, cutting a lot
> of sunlight at Titan's surface.

Interesting. So on a far away planet like Saturn, a long exposure might
be necessary to get properly exposed images.

If I'm not mistaken, there is a planetary probe is on its way to Pluto
(or will be). What ISO will they use and what exposure time to take
photos of Pluto ?
--

On Sun, 01 Jul 2007 14:04:51 -0600, Roger N. Clark (change username
to rnclark) wrote:
>> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
>> Neptune etc., what exposure time would be necessary to take a photo
>> at ISO 100 and F4 or F8 ?
>
> Assuming you wanted to expose an 18% gray card, then
> the exposure would be the square of the relative distance
> of the planet from the sun compared to the earth.
> Don's answer is the only correct one I've seen so far in this
> thread.

There's another correct answer, that there would be no difference
in exposure time. You of all people should know why. <g>

> Going to Venus or Mercury, you have more light, so exposure
> times are shorter, if you can keep your camera from melting!

But what about using the camera on Saturn or Neptune? Wouldn't
conditions there be even more inhospitable? According to one web
page, Jupiter and Saturn are gas giants which have bottomless
atmospheres, with a temperature of about 7000K and a pressure of 2
millibars at a distance of 20,000km below the cloud tops for
Jupiter. Saturn is cooler than Jupiter, but still, this web page
says that on Saturn, "Temperatures of 5000 to 10000 K produce
electrically charged ammonia, methane and water molecules, along
with more complex compounds." Holy melting cameras, Batman!

It's not much better on Neptune, an ice giant considered to be a
sub-class of the gas giants :
> Neptune's temperature at its cloud tops is usually close to -218 °C (-360 °F),
> one of the coldest in the solar system, due to its long distance from the sun.
> However, Neptune's centre is about 7,000 °C (13,000 °F), hotter than the
> sun's surface. This is due to extremely hot gases and rock in the centre.

Where exactly do you want to place the tripod, if in fact you can
find a stable surface to place it? As this wiki webpage notes,
descending below the clouds tops, the temperature rises steadily,
but in the deeper layers of gas, due to its internal energy, it has
"the fastest winds seen in the Solar System", and
> reaching up to around 2100 km/h, near-supersonic speeds. Even
> more typical winds in the banded equatorial region can possess
> speeds of around 1,200 km/h (750 mph).

Also from the above web page, and perhaps useful for determining
one of the answers to Alfred's exposure question :
> Neptune turned out to have the strongest winds of all the solar system's
> gas giants. In the outer regions of the solar system, where the Sun shines
> over 1000 times fainter than on Earth.

So it looks like you might want to use a bulb setting for the
shutter and be prepared to deal with much larger amounts of noise
than is usual for your Earthier shots.

On Sun, 01 Jul 2007 16:08:05 -0500, Allen wrote:
>> So you think the planetary atmosphere wouldn't affect a 18%
>> grey card?
>>
>> Or did you mean exposing from a grey card in space at the
>> same distance drom the sun as the planet - which isn't what
>> the OP asked.
>>
>> Like I said earlier, piece of string until some more
>> parameters are defined.
>
> Do you go out into space with a gray card to determine exposure on
> earth? No. The gray card takes care of local atmospheric conditions etc
> at the time of the reading.

I think the point that John made was that Roger might need to use
his gray card out in space unless a gray card can be found that is
able to survive being exposed to the harsh planetary atmospheres,
which include extremely high temperatures (in some places hotter
than the surface of the Sun) and winds.

In article <>, ASAAR says...
> Where exactly do you want to place the tripod, if in fact you can
> find a stable surface to place it? As this wiki webpage notes,
> descending below the clouds tops, the temperature rises steadily,
> but in the deeper layers of gas, due to its internal energy, it has
> "the fastest winds seen in the Solar System", and

You could be in the cabin of a spaceship, comfortably pointing your
camera with a long zoom to Saturn or Jupiter. Regarding Mars or Pluto,
you might actually step on them and place your tripod on the ground.
Perhaps one they'll offer commercial services to the planets ;-)
--

On Mon, 2 Jul 2007 00:03:02 +0200, Alfred Molon wrote:
> You could be in the cabin of a spaceship, comfortably pointing your
> camera with a long zoom to Saturn or Jupiter. Regarding Mars or Pluto,
> you might actually step on them and place your tripod on the ground.
> Perhaps one they'll offer commercial services to the planets ;-)

On that day, as a measure of respect, I'll not carry my camera
using a strap, but will wear it in a Holst'er.

> "Neptune" was the first piece of music to have a fade-out ending.
> Holst stipulates that the women's choruses are "to be placed in an
> adjoining room, the door of which is to be left open until the last bar
> of the piece, when it is to be slowly and silently closed", and that the
> final bar (scored for choruses alone) is "to be repeated until the sound
> is lost in the distance"[10]. Although commonplace today, the effect
> bewitched audiences in the era before widespread recorded sound -
> after the initial 1918 run-through, Holst's daughter Imogen (in
> addition to watching the charwomen dancing in the aisles during
> "Jupiter") remarked that the ending was "unforgettable, with its
> hidden chorus of women's voices growing fainter and fainter... until
> the imagination knew no difference between sound and silence"

John Bean wrote:
> On Sun, 01 Jul 2007 14:04:51 -0600, "Roger N. Clark (change
> username to rnclark)" <> wrote:
>> and if
>> it has an atmosphere, the absorption of sunlight through
>> the atmosphere.
>
> So you think the planetary atmosphere wouldn't affect a 18%
> grey card?

That's why I said "absorption of sunlight through
>> the atmosphere." In the case of the earth, absorption
is about 15% (a little more in the blue; a little
less in the red). That's about 0.2 stop.
Mars has more of a problem with scattering by red
dust in the atmosphere. Titan (moon of Saturn)
has both more absorption and scattering. The absorption
is several stops (I don't remember the exact number
off the top of my head) in the visible.
> Or did you mean exposing from a grey card in space at the
> same distance drom the sun as the planet - which isn't what
> the OP asked.

No that is not what I meant.
> Like I said earlier, piece of string until some more
> parameters are defined.

Since "it is done all the time" these are well understood
and well modeled problems.

Alfred Molon wrote:
> In article <>, Roger N. Clark (change username
> to rnclark) says...
>
>> For example, Saturn is 9.5 times further from the sun than
>> the earth, so sunlight is 9.5*9.5 times fainter, or about
>> 90. So sunny f/16 rule on earth becomes about sunny f/1.8
>> on Saturn. But on the Icy moons, the reflectivity is near
>> 100% so you gain about 5x in brightness, so exposures would
>> be more like sunny f/4 rule. But on dark moons like Phoebe,
>> where reflectivity is only a couple percent, you lose
>> another factor of 10 over an 18% gray card, so the rule
>> becomes about sunny f/0.5! On Titan, the situation is made
>> difficult by the thick smog in the atmosphere, cutting a lot
>> of sunlight at Titan's surface.
>
> Interesting. So on a far away planet like Saturn, a long exposure might
> be necessary to get properly exposed images.

Definitely. If you are in orbit taking pictures of the planet
(e.g.like Cassini is doing now), exposures are about 90x longer.
If you go down into the atmosphere, it gets worse as the
atmosphere absorbs light.
> If I'm not mistaken, there is a planetary probe is on its way to Pluto
> (or will be). What ISO will they use and what exposure time to take
> photos of Pluto ?

It called New Horizons and recently flew past Jupiter, and has
another 5+ years to get to Pluto. Like most planetary
cameras, there are no f/stops now ISO settings on the cameras.

Here is how it generally works. Cameras are calibrated
with known light sources on the ground in a vacuum
chamber (to simulate space) to calibrate the number
of photons for each level (lowest bit) in the A/D
converter. This is called photons/DN (data number).
Then checked again using stars after launch.
(This is similar to what I've been doing with
DSLRs, see
Digital Cameras:
Counting Photons, Photometry, and Quantum Efficiencyhttp://www.clarkvision.com/imagedetail/digital.photons.and.qe

Then when at the planet, the spectrum of the sun
is used to predict for the viewing geometry
(are you taking a picture of the solar noon point,
or near sunrise or sunset), and calculate the distance
from the sun, the transmission of any filters used,
the reflectance of the planet, and absorption by the atmosphere
to get the number of photons /second incident
on the sensor. Then you decide how much headroom you
want (typically with a 12-bit A/D) and calculate the exposure,
then send the command to the spacecraft. Some cameras
extend into the infrared, and because solar flux is lower,
a second even longer exposure is needed for imaging
at those wavelengths.

Roger N. Clark (change username to rnclark) wrote:
> Alfred Molon wrote:
>> If I'm not mistaken, there is a planetary probe is on its way to Pluto
>> (or will be). What ISO will they use and what exposure time to take
>> photos of Pluto ?
>
> It called New Horizons and recently flew past Jupiter, and has
> another 5+ years to get to Pluto. Like most planetary
> cameras, there are no f/stops now ISO settings on the cameras.

I forgot to answer the question in my last reply.
Pluto is about 20 times
further from the sun than the Earth, so exposures will be
about 20*20 = 400 times longer than on Earth.
So a 1/100 second Earth exposure becomes a 4 second
exposure at Pluto.

Roger N. Clark (change username to rnclark) wrote:
> Roger N. Clark (change username to rnclark) wrote:
>> Alfred Molon wrote:
>
>>> If I'm not mistaken, there is a planetary probe is on its way to
>>> Pluto (or will be). What ISO will they use and what exposure time to
>>> take photos of Pluto ?
>>
>> It called New Horizons and recently flew past Jupiter, and has
>> another 5+ years to get to Pluto. Like most planetary
>> cameras, there are no f/stops now ISO settings on the cameras.
>
> I forgot to answer the question in my last reply.
> Pluto is about 20 times
> further from the sun than the Earth, so exposures will be
> about 20*20 = 400 times longer than on Earth.
> So a 1/100 second Earth exposure becomes a 4 second
> exposure at Pluto.
>
> Roger
Oops, that should have been 30 to 50 times further
(an elliptical orbit), so 900 to 2500 times fainter
sunlight for Pluto. So the Earth exposure of 1/100 second
would turn into 9 to 25 seconds depending
on where Pluto was in its orbit.

ASAAR wrote:
> On Sun, 01 Jul 2007 14:04:51 -0600, Roger N. Clark (change username
> to rnclark) wrote:
>
>>> Just curious - assuming you were on a planet, Mars, Saturn, Venus,
>>> Neptune etc., what exposure time would be necessary to take a photo
>>> at ISO 100 and F4 or F8 ?
>> Assuming you wanted to expose an 18% gray card, then
>> the exposure would be the square of the relative distance
>> of the planet from the sun compared to the earth.
>> Don's answer is the only correct one I've seen so far in this
>> thread.
>
> There's another correct answer, that there would be no difference
> in exposure time. You of all people should know why. <g>

With changing light levels you can do three things
with a given camera:
1) change exposure time,
2) change the aperture, and
3) "change the ISO."

But spacecraft cameras and science teams are concerned
with signal/noise ratios and thus track the number of
photons. No spacecraft camera that I know of is calibrated in
ISO. Some have 2 gain states, if their lowest gain
state does not adequately digitize the read noise.
Nor do any spacecraft cameras I know of have
iris apertures that can be changed.

For example the Cassini VIMS instrument has 2 gain states,
but because the lowest gain state adequately digitizes
the read noise, the higher gain state has not yet been used
since Saturn orbit insertion. Here is a recent image from VIMS:http://apod.nasa.gov/apod/ap070627.html
>
>> Going to Venus or Mercury, you have more light, so exposure
>> times are shorter, if you can keep your camera from melting!
>
> But what about using the camera on Saturn or Neptune? Wouldn't
> conditions there be even more inhospitable?

It depends on how deep into the atmosphere you go. It is kind
of like the earth's oceans. Go down a few feet and no problem.
But the deeper you go, the higher the pressure.
There is no known surface on Jupiter, Saturn, Neptune,
or Uranus. But what it really is like is unknown as
all we currently have regarding the deep interiors is
just theory with no data.
>According to one web
> page, Jupiter and Saturn are gas giants which have bottomless
> atmospheres, with a temperature of about 7000K and a pressure of 2
> millibars at a distance of 20,000km below the cloud tops for
> Jupiter. Saturn is cooler than Jupiter, but still, this web page
> says that on Saturn, "Temperatures of 5000 to 10000 K produce
> electrically charged ammonia, methane and water molecules, along
> with more complex compounds." Holy melting cameras, Batman!
>
>
> http://opensourceschools.org/article.php?story=20030512174818794&mode=print

There is one mistake: 2 millibars. For that depth, it is probably
like 2 megabars (a bar = 1 earth atmosphere in pressure).
> It's not much better on Neptune, an ice giant considered to be a
> sub-class of the gas giants :
>
>> Neptune's temperature at its cloud tops is usually close to -218 °C (-360 °F),
>> one of the coldest in the solar system, due to its long distance from the sun.
>> However, Neptune's centre is about 7,000 °C (13,000 °F), hotter than the
>> sun's surface. This is due to extremely hot gases and rock in the centre.
>
> Where exactly do you want to place the tripod, if in fact you can
> find a stable surface to place it? As this wiki webpage notes,
> descending below the clouds tops, the temperature rises steadily,
> but in the deeper layers of gas, due to its internal energy, it has
> "the fastest winds seen in the Solar System", and
>
>> reaching up to around 2100 km/h, near-supersonic speeds. Even
>> more typical winds in the banded equatorial region can possess
>> speeds of around 1,200 km/h (750 mph).
>
> http://en.wikipedia.org/wiki/Neptune
>
> Also from the above web page, and perhaps useful for determining
> one of the answers to Alfred's exposure question :
>
>> Neptune turned out to have the strongest winds of all the solar system's
>> gas giants. In the outer regions of the solar system, where the Sun shines
>> over 1000 times fainter than on Earth.
>
> So it looks like you might want to use a bulb setting for the
> shutter and be prepared to deal with much larger amounts of noise
> than is usual for your Earthier shots.

This reminds me of the time I was talking to 2nd grade
school children (no implied education level here, just
a funny story). One kid asked me "how many houses could
you fit on Jupiter" I answered "That is a trick question!
Jupiter has no surface so you can't build any houses on Jupiter.
As you go deeper and deeper into Jupiter's atmosphere, it just
becomes thicker, then more and more like soup, then mud and you
keep sinking."

Then another side question. The above image
of Saturn from VIMS is a digital mosaic with the infrared
part of the "camera," but the vims IR
instrument is a single physical spatial pixel but it
records 352 wavelengths simultaneously (Foveon sensors
only do 3). The vims scans an image 64 x 64 pixels per
full frame. Is vims a 0.004 megapixel camera (64*64/1,000,000)
or a 1.4 megapixel camera (64*64*352), or a 1/1,000,000
(one millionth) megapixel camera? The foveon people
would call it a 1.4 megapixel camera. I call it a
1/1,000,000 megapixel camera. ;-)

Share This Page

Welcome to Velocity Reviews!

Welcome to the Velocity Reviews, the place to come for the latest tech news and reviews.

Please join our friendly community by clicking the button below - it only takes a few seconds and is totally free. You'll be able to chat with other enthusiasts and get tech help from other members.
Sign up now!